The invention relates to line loading for a rotating grass trimmer head and, more particularly, to grass trimmer heads and line loading schemes for easily and securely installing independent cutting blades in a desired orientation.
The invention is particularly suited for use with cutting blades including a non-circular or non-symmetrical cross-section, in particular an aerodynamic cross-section. With such cutting line, it is possible to achieve vastly improved cutting results as well as other advantages in vegetation cutting string, devices and methods. An exemplary vegetation cutter using such aerodynamic line is disclosed in U.S. Pat. No. 5,761,816, the disclosure of which is hereby incorporated by reference. Further examples and applications of cutting blades utilizing an aerodynamic cross-section are disclosed in U.S. Pat. No. 5,996,233, U.S. Pat. No. 6,161,292, U.S. Pat. No. 6,176,015, U.S. Pat. No. 6,314,848, U.S. Pat. No. 6,415,585, and U.S. Pat. No. 6,862,871, the disclosures of all of which are hereby incorporated by reference.
In the grass trimmer heads utilizing flexible monofilament lines or flexible line blades including symmetrical or non-symmetrical hinges, loading and/or replacing the individual cutting lines/blades can be burdensome, particularly in the field, since the lines are required to be adequately and independently secured in the trimmer head. Additionally, significant advantages can be achieved by varying the orientation of the aerodynamic cutting line depending on desired use. It would thus be beneficial to provide a trimmer head that can accommodate the line in multiple orientations so that different lines are not required for different uses.
Rapid line loader heads for grass trimmers (currently on the market) all require added mechanical mechanism(s) that self-lock conventional monofilament line only with physically moving component parts that ‘compress’ or ‘bite’ into the line segment as their frictional means for line retention within the head. Such heads are convenient and attractive when the trimmer user wants to avoid a complex and frustrating process when needing to replace worn trimmer line. These rapid loaders simplify the line replenishment process, which is often complicated by snarling bundles of snagged line, or if using precut lengths by having to repetitively replace worn out line, or having to remove component parts making the process further frustrating with numerous types of complex systems that jam when feeding or are otherwise very complex to wind and reload.
The precut line segment is inserted into an outlet and internally retained or gripped by the movement and squeezing of a rotating or sliding type of gripping mechanism. They generally involve a one way direction first through the outlet but upon the line's wearing out and needing replacement, it normally cannot be reversed back through the outlet unless its mechanical retainer is in some manner mechanically relocated or dislodged from its compressive grip on the line. If there is no reversing removal feature, the worn line must be pulled away from the gripping direction and more frequently toward the center of the head in the same general direction as it was first inserted into the head. The design of the head is therefore often compromised to require a large or interfering removal zone in another place (generally in the center of the head) other than the line outlet where the initial insertion was required. This causes the designer to limit the important provision for a ground supporting bubble or sliding curvature at the base of the head where it contacts the ground.
Additionally, the grippers will frequently allow the line to slip out for numerous potential reasons, thus disabling the desirable features and any further cutting/trimming because the line is forced out by centrifugal force or impacting loads during string cutting operations without being retained. The causes for lost grip are related to potential jamming, loss of spring force, loss of gripper sharpness, misalignment, foreign debris blocking the mechanism, friction preventing the needed movement of the mechanisms, excessive mass and high centrifugal forces onto the line, geometry of the line, and more.
Moreover, these heads are very costly because they require additional and multiple precision components that are costly themselves to manufacture and labor intensive to assemble into a final product. These precision parts have to be mounted to strong supporting posts or accurately preformed slots to assure their reliable gripping functions within the working mechanism.
Such mechanisms work for generally most symmetrical lines but are less capable in accepting and adequately gripping non-circular or otherwise non-symmetrical line shapes such as rectangular or asymmetrical sections such as, tear drop, or elliptical, etc. Additionally, such mechanisms do not allow insertion and retention means that will allow a desired orientation of a particular profile when the frontal curvature or cutting edges need to be directed along the general operational or cutting plane.